Andyfteeze wrote:The foil works because it reflects the infrared radiation. However it still conducts heat!The best you can hope for is to ventilate the roof space and foil the ceiling.A good analogy is. Frypan in shade, frypan in sun! Look at the frypan in the shade as ambient temperature under the foil and frypan in the sun as what the sun is doing to your roof. Because in your situation, you have no ceiling space, the foil reflects the heat very well, lol, but it will still conduct the heat although not as much as the tin roof on its own due to its light mass relative to the roof.

Sorry you have that wrong.

Physics 101Mass has nothing to do with the situationThe foil has nothing to do with reflection, the back of the foil is brown and the back is faceing the hot roof. It has nothing to do with conduction as the foil is only in contact with the beams.It is all about radiation, the roof gets very hot and the back, grey, radiates heat well. The foil being silver is a very poor radiator hence roof 60 degrees C foil 20 to 30 degrees C lower than the roof in full sun.

We have had similar results as sometimes-ww. Our upstairs studio is open to the roof and you can never feel any heat radiation from up there. On a ladder, it barely feels warm when you put your hand against the foil backing even on the hottest of days. The foil backed insulation is definitely worth the cost even for an awning.

Hahaha Jerome what are we to do with you, lol. Right conclusion for all the wrong reasons.1/ whats under the brown colour? If its paper, its a good insulator to start with. Then under that is an aluminium surface, no? aliminium conducts heat, no? Why is that sauce pan in your hand made of aluminium? What , doesn't conduct heat to cook my food? Mass does come into play. The shear minimal Mass means it holds little heat and so the rate of heat transference is low.Think of it this way, a tap with a small drip, there is great pressure on the other side, but only a small drip gets through.My statement stands, it still conducts heat, but so small relative to ambient AND the roof, its dissipated quickly.2/ sure the shiny aliminium surface reflects ir radiation, but not the big ticket item here.Imagine if the foil was 2mm thick, as a frypan, what would the outcome be? Totally different!!!I stand to be corrected. Come on try me. LolAnyway, we shouldnt be turning this into a physics debate, just that it works and we should be thinking about how to apply this knowledge in a smart way.

Before anymore fables get told about physics 101 and what actually happens when a radiant barrier is put in place it's time to read this: http://energy.gov/energysaver/articles/radiant-barriersIf it is read entirely it might stop both sides being half right and half wrong. And don't forget it depends on the type of foil used......and dust.

Dust only comes into play when the foil can collect dust, mine can't. If you lay foil on top of a ceiling for example then reflection and dust come into play. However there is no way for dust to collect on my foil inless it gets covered in greasy smoke first. So in my application it is only the poor radiation of the foil that comes into play.

Sometimewoodworker wrote:Dust only comes into play when the foil can collect dust, mine can't. If you lay foil on top of a ceiling for example then reflection and dust come into play. However there is no way for dust to collect on my foil inless it gets covered in greasy smoke first. So in my application it is only the poor radiation of the foil that comes into play.

Then your foil is keeping heat in and not doing the job it was intended to do, to put a barrier between you and the outside heat. There's a lot of science at work here including refraction and reflection, mass and convection, just to name a few. It might pay to read the article again.

Sometimewoodworker wrote:Dust only comes into play when the foil can collect dust, mine can't. If you lay foil on top of a ceiling for example then reflection and dust come into play. However there is no way for dust to collect on my foil inless it gets covered in greasy smoke first. So in my application it is only the poor radiation of the foil that comes into play.

Then your foil is keeping heat in and not doing the job it was intended to do, to put a barrier between you and the outside heat. There's a lot of science at work here including refraction and reflection, mass and convection, just to name a few. It might pay to read the article again.

If you look at the photos you will see that apart from not being installed before the roof metal was fitted the foil is functioning in the way it is designed to and it is working.

Andyfreeze seems to think that a thin piece of brown paper provides good insulation and if it did it would be a wonderful discovery, would revolutionise the insulation market, and save lots of people los of money

You seem to be saying that it should be reflecting the heat back, it doesn't as the backing which is to the heat source is brown paper.

You then seem to postulate that it can't work but it does.

I am proving that it is the poor ability to radiate heat from a silvered surface place horizontally down that works.I am not getting into other kinds of placement and the problems they may incur, or other varieties of foil or other kinds of insulation with or without foil. If you want to discuss that start your own thread.

My foil has no ability to insulate it is just brown paper backed foil. I have conclusive proved that when placed silver face down it reduces the heat radiation by up to 27 degrees C. Radiant heat is the problem. Not conducted heat or convected heat. There are no closed areas to let convected heat build up. There is nowhere for the heat to be conducted to. Mass is not a significant factor, if it were then a simple sheet of paper would work just as well as the foil. QED it is the poor radiation of silvered surfaces.

Sometimewoodworker wrote:You seem to be saying that it should be reflecting the heat back, it doesn't as the backing which is to the heat source is brown paper.

You then seem to postulate that it can't work but it does.

Are you saying that the scientists at the US Energy Department that wrote the article are wrong? I've seen your photos and you have the wrong side up if it's brown paper. Mass does matter, it disipates the energy over a wider area. That's what we are talking about, energy.

Sometimewoodworker wrote:You seem to be saying that it should be reflecting the heat back, it doesn't as the backing which is to the heat source is brown paper.

You then seem to postulate that it can't work but it does.

Are you saying that the scientists at the US Energy Department that wrote the article are wrong? I've seen your photos and you have the wrong side up if it's brown paper. Mass does matter, it disipates the energy over a wider area. That's what we are talking about, energy.

I'm not talking about energy in general you are and it's irrelevant. I'm talking about reducing radiated heat.

The article you link to doesn't address my point, mass is a red herring as there is very little. I'm interested in reducing radiated heat so brown up silver down is correct and it works.

A double sided silver foil might perform better, then the top would be reflecting and the bottom wouldn't be radiating but in my situation I've got single sided so silver side down is correct in my roof.

Sometimewoodworker wrote:I'm not talking about energy in general you are and it's irrelevant. I'm talking about reducing radiated heat.

The article you link to doesn't address my point, mass is a red herring as there is very little. I'm interested in reducing radiated heat so brown up silver down is correct and it works.

A double sided silver foil might perform better, then the top would be reflecting and the bottom wouldn't be radiating but in my situation I've got single sided so silver side down is correct in my roof.

So just let me get this clear, you're claiming the radiated heat comes from the floor and not the roof and that the mass of the roof has no bearing? If heat isn't energy then what is? If the radiated heat is coming from your roof then the barrier (silver foil) should face the source of the heat to radiate it back.... but in your case that's the floor.The article I linked to totally addressed your point, in fact it was addressed in the first three paragraphs, but it would appear you are in denial and therefore all scientific logic is thrown out the window. The words here are "reflective" and "barrier" the reflective side causes the barrier between the heat source (the roof), but in your case the floor, and radiates the heat back. There is no hell's fires like the kitchen but you appear to have taken that one step further.Where do you think the energy to heat the roof comes from if not the sun. Are you claiming the sun is now irrelevant as a heat source? And are you also claiming that the mass of the roof also has no bearing on the amount of heat radiated through it.I'm sorry sometimewoodworker, on this you are wrong, totally wrong.

I dont think you quite understand the processes involved here.The roof is heated by the sun. The roof then radiates heat down to the foil. The foil with a brown backing. The brown backing, if its paper it will have a SMALL insulating capability. FACT, paper is a good insulator. The amount used here is very small, so its effect is small. Dont put words in my mouth please. There is no need to over extrapolate my statement of fact. There are plenty of research papers to prove it. ( pun)The aluminium itself does conduct heat , BUT because of its very low mass, it ABSORBS very little ENERGY which it then radiates on the other side. The amount of energy getting through is very small relative to ambient temperature. Therefore sitting under the roof as modified , is like siting in the shade. If the roof is 60c and the shade is 35c, thats what you will measure. 35c. Ambient temp.Heat is energy, dont know who told you otherwise.I dont think there would be a huge difference in the foils performance either way. A difference yes, but small relative to other factors.The foil is NOT reflecting heat back to any significant degree. Thats not the main physics at play in this situation.Its the MASS of the foil, or lack of, which is doing the job.As i stated previously, if the foil was 2mm thick, it would act like a frypan with the gas on high. Silver or not it will heatup, which proves that its a conductor of heat and the mass is IMPORTANT We now move to physics 10101No one is saying it doesnt work, just your reasoning and conclusion is wrong.

Sometimewoodworker wrote:I'm not talking about energy in general you are and it's irrelevant. I'm talking about reducing radiated heat.

The article you link to doesn't address my point, mass is a red herring as there is very little. I'm interested in reducing radiated heat so brown up silver down is correct and it works.

A double sided silver foil might perform better, then the top would be reflecting and the bottom wouldn't be radiating but in my situation I've got single sided so silver side down is correct in my roof.

So just let me get this clear, you're claiming the radiated heat comes from the floor and not the roof and that the mass of the roof has no bearing? If heat isn't energy then what is? If the radiated heat is coming from your roof then the barrier (silver foil) should face the source of the heat to radiate it back.... but in your case that's the floor.The article I linked to totally addressed your point, in fact it was addressed in the first three paragraphs, but it would appear you are in denial and therefore all scientific logic is thrown out the window. The words here are "reflective" and "barrier" the reflective side causes the barrier between the heat source (the roof), but in your case the floor, and radiates the heat back. There is no hell's fires like the kitchen but you appear to have taken that one step further.Where do you think the energy to heat the roof comes from if not the sun. Are you claiming the sun is now irrelevant as a heat source? And are you also claiming that the mass of the roof also has no bearing on the amount of heat radiated through it.I'm sorry sometimewoodworker, on this you are wrong, totally wrong.

On this I am right right right

http://web.ornl.gov/sci/ees/etsd/btric/RadiantBarrier/rb2.shtml

The article you link to is also not comprehensive and gives an incorrect reason "minimize dust accumulation" for the orientation of foil.

It's easier to incorporate radiant barriers into a new home, but you can also install them in an existing home, especially if it has an open attic. In a new house, an installer typically drapes a rolled-foil radiant barrier foil-face down between the roof rafters to minimize dust accumulation on the reflective faces (double-faced radiant barriers are available). This is generally done just before the roof sheathing goes on, but can be done afterwards from inside the attic by stapling the material to the bottom of the rafters.

You are fixated on a misunderstanding. And wriggling around to try to prove your misunderstanding is correct.

The mass of the roof, which I was not talking about, is not relevant.

I have never claimed as you do that the foil I use is reflecting heat.

The foil I use works because the silver side is a very poor RADIATOR of heat.

Andyfteeze wrote:The roof is heated by the sun. The roof then radiates heat down to the foil. The foil with a brown backing. The brown backing, if its paper it will have a SMALL insulating capability. FACT, paper is a good insulator. The amount used here is very small, so its effect is small.

No argument there

Andyfteeze wrote:The aluminium itself does conduct heat , BUT because of its very low mass, it ABSORBS very little ENERGY which it then radiates on the other side.

Here is where you are getting the physics wrong it works not because the mass is low. If that were the case then a simple sheet of brown paper would be just as effective.

If it radiates all the heat energy it gets then it would be a "blackbody" Planck's law

A blackbody absorbs all radiation incident on its surface and emits radiation based on its temperature.

The physics involved here is shiny metal surfaces which have low emissivities in the far infrared.

If the foil was double sided then the high reflectivity on the upper side would also come into play.

Andyfteeze wrote:The amount of energy getting through is very small relative to ambient temperature. Therefore sitting under the roof as modified , is like siting in the shade. If the roof is 60c and the shade is 35c, thats what you will measure. 35c. Ambient temp.

Again of course that is true and why it works.

Andyfteeze wrote:Heat is energy, dont know who told you otherwise.

Sure that is RR confusing things

Andyfteeze wrote:I dont think there would be a huge difference in the foils performance either way. A difference yes, but small relative to other factors.The foil is NOT reflecting heat back to any significant degree. Thats not the main physics at play in this situation.

I agree I never said it does that was RR

Andyfteeze wrote:Its the MASS of the foil, or lack of, which is doing the job.As i stated previously, if the foil was 2mm thick, it would act like a frypan with the gas on high. Silver or not it will heatup, which proves that its a conductor of heat and the mass is IMPORTANT

The conductivity isn't in play here neither is the mass, or lack of it, aluminium is a good conductor of heat. However a polished aluminium surface coated with thin plastic film to prevent oxidation is an extremely poor emitter of heat (it is also a good reflector but that property isn't used in this situation as my foil is single sided.

Andyfteeze wrote:We now move to physics 10101No one is saying it doesnt work, just your reasoning and conclusion is wrong.

My reasoning and conclusion is sound, but my ability to explain may not be as good.

Andyfteeze wrote:Just to rub it in, lol.Is the foil hot to touch? Proves its conducting heat. If it was just reflecting , it would be COOL!!!Physics 10102

As I have continued to say radiation is important not reflection or conduction.